1. Field of the Invention
The present invention relates to a microwave power source apparatus for a microwave oscillator and a control method therefor, and more particularly, to a microwave power source apparatus for a microwave oscillator comprising means for automatically adjusting a progressive wave power of a microwave outputted from the microwave oscillator to a predetermined desirable adjustment value, more precisely, and a control method therefor.
2. Description of the Prior Art
FIG. 15 shows a conventional microwave power source apparatus and peripheral units thereof.
Referring to FIG. 15, a microwave from a microwave oscillator 100 is outputted through an isolator 101 and a main rectangular waveguide 102a of a directional coupler 102 to a microwave load 110. The directional coupler 102 comprises the main rectangular waveguide 102a and a sub-rectangular waveguide 102b which are coupled with each other, and the sub-rectangular wave guide 102b comprises a rectangular waveguide 102ba for outputting a portion of the progressive wave of the microwave and a rectangular waveguide 102bb for outputting a portion of the reflected wave of the microwave. The end portion of the rectangular waveguide 102ba is terminated with a non-reflection resistive terminator 103, and the end portion of the rectangular waveguide 102bb is terminated with a non-reflection resistive terminator 104. A portion of the progressive wave of the microwave propagating in the rectangular waveguide 102ba is detected by a diode DI11, and the detected voltage signal is outputted to a voltage detector 111. On the other hand, a portion of the reflected wave of the microwave propagating in the rectangular waveguide 102bb is detected by a diode DI12, and the detected voltage signal is outputted to a voltage detector 112.
The voltage detector 111 detects and amplifies the inputted voltage signal, and outputs it to a linear correction circuit 131. Further, the voltage detector 112 detects and amplifies the inputted voltage signal, and outputs it to a linear correction circuit 132. Since the respective voltages detected by the diodes DI11 and DI12 are not directly proportional to the progressive wave power Pi and the reflected wave power Pr of the microwave propagating in the main rectangular waveguide 102a of the rectangular waveguide 102, respectively, the linear correction circuits 131 and 132 corrects the DC voltages outputted from the voltage detectors 111 and 112 so that the output voltages from the correction circuits 131 and 132 are directly proportional to the progressive wave power Pi and the reflected wave power Pr of the above-mentioned microwave. The corrected DC voltage from the linear correction circuit 131 is inputted to a DC voltmeter M11 for indicating the practical progressive wave power Pi and an inverted input terminal of an error amplifier AMP of a differential amplifier. On the other hand, the corrected DC voltage from the linear correction circuit 132 is inputted to a DC voltmeter M12 for indicating the practical reflected wave power Pr.
A DC power source 122 for setting a desirable progressive wave power comprises a variable resistor VR changes the output DC voltage thereof according to change in the resistance of the variable resistor VR, and outputs the DC voltage to a non-inverted input terminal of the error amplifier AMP. Further, the error amplifier AMP amplifies a difference voltage obtained by subtracting the DC voltage inputted to the inverted input terminal thereof from the DC voltage inputted to the non-inverted input terminal thereof, and outputs the amplified DC difference voltage as a control voltage through a driving amplifier DA to a high voltage DC power source circuit 120. The high voltage DC power source circuit 120 changes the current from a high voltage DC power source provided therein according to the inputted control voltage, and outputs the DC electric power of a relatively high voltage to the microwave oscillator 100 as a DC power for an anode power thereof. On the other hand, a DC power source circuit 121 supplies a DC electric power of a relatively low voltage to the microwave oscillator as a DC power for a heater thereof.
In the conventional microwave power source apparatus constituted as described above, the difference voltage between the DC voltage directly proportional to the progressive wave power Pi outputted from the linear correction circuit 131 and the DC voltage directly proportional to a desirable adjustment value of the progressive wave power set using the variable resistor VR and outputted from the DC power source 122 is amplified by the error amplifier AMP and the driving amplifier DA, and the amplified DC voltage is applied as the control voltage to the high voltage DC power source circuit 120. Then, the current of the high voltage DC power source for the anode voltage source supplied from the high voltage DC power source circuit 120 to the microwave oscillator 100 is controlled according to the control voltage.
In this feed-back control system, the progressive wave power of the microwave propagating from the microwave oscillator 100 in the main rectangular waveguide 102a of the directional coupler 102 is controlled so as to become the desirable adjustment value of the progressive wave power set using the variable resistor VR of the DC power source 122.
In other words, as shown in FIG. 16, an automatic output power adjusting process executed by the conventional microwave power source apparatus shown in FIG. 15 includes:
(a) step S101 of detecting the progressive wave and reflected wave voltages of the microwave by the directional coupler 102;
(b) step S102 of converting the detected progressive wave and reflected wave voltages into the DC voltage corresponding to the powers thereof by the linear correction circuits 131 and 132;
(c) step S103 of amplifying the difference voltage between the DC voltage corresponding to the progressive wave power and the set DC voltage corresponding to the desirable adjustment value of the progressive wave power by the error amplifier AMP and the driving amplifier DA; and
(d) step S104 of controlling the anode current of the magnetron of the microwave oscillator 100 based on the amplified difference voltage.
However, in the above-mentioned microwave power source apparatus for controlling to adjust the progressive wave power of the microwave outputted from the microwave oscillator 100 into a predetermined desirable adjustment value, since there is used the directional coupler 102 in order to detect a portion of the progressive wave power of the microwave and a portion of the reflected wave power thereof, the size of the system including the microwave power source apparatus and the peripheral units thereof becomes relatively large, and then, the above-mentioned system can not be miniaturized.
On the other hand, there is disclosed in U.S. Pat. No. 5,079,507 an automatic microwave impedance adjusting apparatus for a microwave load connected to a microwave oscillator through a microwave transmission line, and an automatic microwave impedance adjusting method therefor. In the U.S. Patent, as shown in FIG. 17, the automatic microwave adjusting method includes:
(a) step S201 of inputting a desirable reflection coefficient .GAMMA.s to be adjusted;
(b) step S202 of calculating an admittance Ys=Gs+jBs corresponding to the desirable reflection coefficient .GAMMA.s and an admittance Ys'=Gs'+jBs' when the phase is inverted from the admittance Ys;
(c) step S203 of detecting DC voltages corresponding to the absolute values of the voltage standing wave .vertline.Va.vertline., .vertline.Vb.vertline. and .vertline.Vc.vertline. using three probes located apart by .lambda.g/6 from each other;
(d) step S204 of calculating a reflection coefficient .GAMMA.o at a predetermined reference point based on the detected three DC voltages corresponding to the absolute values of the voltage standing wave;
(e) step S205 of calculating insertion lengths of three stubs to be inserted into a rectangular waveguide of the microwave transmission line which are located apart by .lambda.g/4 from each other, based on the calculated reflection coefficient .GAMMA.o and the inputted desirable reflection coefficient .GAMMA.s; and
(f) step S206 of adjusting the impedance using at least two of the three stubs by inserting them by the calculated insertion lengths, respectively.
In FIG. 1 of the U.S. Patent, there is disclosed that the automatic microwave impedance adjusting apparatus comprises a power detector 10d for detecting a microwave power and a power controller 10c for controlling the microwave oscillator 10 to output a desirable output power based on the detected microwave power. However, since the microwave power in a rectangular waveguide 12 is detected and the output power is controlled based on the detected microwave power, in other words, since the output power is not controlled based on an accurate progressive wave power of the microwave propagating therein, the output power can not be controlled stably and precisely.